An electroluminescent lamp (EL-lamp) is a light source that is typically used for portable (battery operated) electronic devices. An EL-lamp is constructed similar to a capacitor in that it has a dielectric positioned between two electrodes. In an EL-lamp, one of the electrodes is transparent. Typically, a phosphor powder is used to radiate light when a strong electrical field is applied across it. The phosphor powder may be contained in the dielectric layer or it may be in a separate layer that is adjacent the dielectric layer. The EL-lamp is illuminated when an alternating current (AC) is applied across the electrodes. An integrated driver circuit (an EL driver) is typically used to convert direct current (DC) from the battery to a desired AC current. An example of a three port EL driver is described in U.S. Pat. No. 5,347,198 to Kimball which is incorporated herein by reference.
In a typical EL driver application, the EL driver will deliver a voltage to the lamp on the order of 160 to 240 volts peak to peak. The lamp frequency is typically 100 to 800 HZ. If EL-lamps are used as backlights for color displays, a white panel will be used that may require peak-to-peak voltage swings as high as 400V. In this type of application the displays tend to be relatively large. Accordingly, the load will need to store a large amount of energy at each peak to work properly.
It is desired that the EL-lamp and its associated EL driver circuit to generate the maximum amount of illumination with minimum power drain. The efficiency of a typical integrated EL driver is generally less than 35%. This efficiency is calculated as the energy delivered to the load divided by the energy drained from the battery. Accordingly, it is desired in the art to improve the efficiency of EL-drivers.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an efficient EL-driver.